The invention relates to an automated gear transmission, more particularly to a dual-clutch transmission having two input shafts arranged mutually essentially concentrically for use in a motor vehicle.
Various automated gear transmissions, dual-clutch transmissions for motor vehicles, are known from the prior art. Of these, numerous embodiments include two concentric input shafts and two output shafts for driving the vehicle. It is also known from DE 199 44 879 A1, that an embodiment with two input shafts arranged essentially concentrically to each other may be provided with only one output shaft for mechanical design simplification and to reduce the transmission's installation space requirement. Disclosed in that publication is a dual-clutch transmission intended for a motor vehicle and comprising two mutually concentric input shafts and one output shaft, with the first and second input shafts being each connectable to a drive shaft via first and second clutches, respectively. The first input shaft is engageable with the output shaft via at least one first pair of gear wheels, whereas the second input shaft is engageable with the output shaft via at least one second pair of gear wheels. In order to achieve an advantageously compact design for front longitudinal mounting in the engine compartment of a motor vehicle, it is intended that the first input shaft should be in the form of a solid shaft while said second input shaft should be of hollow shaft design. The first input shaft should be arranged within the second input shaft. The input shafts and output shaft should each be disposed in a direction essentially parallel to the longitudinal axis of the vehicle, while the first and second clutch should be arranged radially relative to each other.
One embodiment of this arrangement comprises seven forward speeds. Preferably, a separate auxiliary shaft is provided for implementing a reverse gear. According to further design features, the first input shaft carries the respective gear wheels for the seventh, fifth, third and first speeds, in that order, while the second input shaft may carry the respective gear wheels for the second, fourth and sixth speed, in that order. Provision is made in this arrangement for the first and third speed, fourth and sixth speed, fifth and seventh speed, and second and reverse speed to share a common sliding sleeve in each case for selective shifting of the above-mentioned speeds. This feature is intended to achieve a particularly compact design of the dual-clutch transmission. The two clutches may be in the form of multi-plate clutches, whereby a compact radial clutch with a clutch housing is said to be implemented. Depending on how the clutches are configured in this arrangement, the radially inward or radially outward clutch may be designed as a start-up clutch.
A dual-clutch transmission of the above design is alleged to lend itself to compact installation in a front longitudinal configuration in the engine compartment of a motor vehicle, given that the first input shaft is a solid shaft while the second input shaft is in the form of a hollow shaft, one being arranged within the other. Moreover, there is said to be provided only one output shaft extending, like the input shafts, in the longitudinal direction of the vehicle. It is stated to be a decisive feature that the necessary clutches are arranged radially and no longer sequentially relative to each other, whereby the requisite installation space in the vehicle's longitudinal direction is said to be minimized.
A particular disadvantage of this known embodiment of a dual-clutch transmission for a motor vehicle is that the design integration of the reverse speed into said transmission should be improved. Overlap of the individual speed-change gears will regularly occur due to the defined gear positions associated with the integration of the reverse speed. As a result of these defined gear positions in a dual-shaft powershift transmission, a normal reverse speed—as implemented via an axially displaceable sliding gear wheel—cannot be achieved without overlap, or a poor transmission ratio of the individual speed-change gears, or without negatively affecting the transmission dimensions.